Field
One feature relates to communication systems, and more particularly, to a method for differentiating retransmission policy within a plurality of protocol data units.
Background
In transmissions between a transmitter and a receiver, the transmitter may transmit a block (plurality) of frames, such as Media Access Control (MAC) Protocol Data Units (MPDUs), without requesting individual acknowledgements for each transmitted MPDU. This method is referred to as Block Acknowledgements, as defined in Institute of Electrical and Electronics Engineers (IEEE) Standard 802.11n-2009. The MPDUs may be aggregated as an Aggregated MPDU (A-MPDU), to allow multiple MPDUs to be transmitted as part of the same Physical Layer (PHY) Protocol Data Unit (PPDU). The receiver of the data stream may reply with a Block Acknowledgement (BA) which acknowledges the receipt of one or more frames at once. For instance, the BA may acknowledge received frames by setting an associated bit inside an Ack bitmap that is carried by the BA. The location of the bit inside the bitmap corresponds to the sequence number of the received frame. A receiver forwards MPDUs up the protocol stack according to their sequence number, but when an MPDU is not received, the receiver waits either until the MPDU with that sequence number has been retransmitted, or until the queue has been purged by a Block Acknowledgement Request (BAR) frame that increases the sequence number to beyond the missing MPDU. The BAR frame is transmitted by the source of the data stream when it no longer will retransmit old sequence numbers. So while the current BA rules allow for discarding frames at the receiver by purging the queue through a Block Acknowledgement Request (BAR) frame, but the discarding rules are the same for all frames in a single Block Acknowledgement (BA) agreement. For instance, a BAR frame may be transmitted by the transmitter to the receiver to request for a BA to be sent or to purge the queue at the receiver up until an indicated sequence number. Frames with a sequence number older than the sequence number indicated in a BAR frame will not be retransmitted. However, it is not possible to exclude individual frames from this policy.
According to one example, in a video stream transmitted using User Datagram Protocol (UDP), some frames may contain more important information than other frames. Frames which contain less important information may be dropped (i.e. not retried or not tried at all) sooner than frames which contain important information. Current BAR frames do not permit such per frame policy to be specified.
Therefore, a solution is needed that allows defining a policy whereby individual frames within a block of frames can be marked for retransmission while other frames are purged.